Đáp án:
7B
Giải thích các bước giải:
\(\begin{array}{l}
C5:\\
\dfrac{{15 + 6x}}{{5x + 10{x^2}}} = \dfrac{{3\left( {5 + 2x} \right)}}{{5x\left( {1 + 2x} \right)}}\\
C6:\\
\dfrac{5}{{3\left( {x - 2} \right)}} = \dfrac{{5\left( {x + 2} \right)}}{{3\left( {x - 2} \right)\left( {x + 2} \right)}}\\
\dfrac{6}{{\left( {x - 2} \right)\left( {x + 2} \right)}} = \dfrac{{6.3}}{{3\left( {x - 2} \right)\left( {x + 2} \right)}}\\
\to A\\
C7:\\
DK:x \ne - 2\\
\dfrac{{{x^2} - 4}}{{{{\left( {x + 2} \right)}^2}}} = 0\\
\to \dfrac{{\left( {x - 2} \right)\left( {x + 2} \right)}}{{{{\left( {x + 2} \right)}^2}}} = 0\\
\to \dfrac{{x - 2}}{{x + 2}} = 0\\
\to x - 2 = 0 \to x = 2\\
\to B
\end{array}\)
